The effect of inspiratory muscles fatigue on postural control in people with and without recurrent low back pain.

STUDY DESIGN: A 2-group experimental design.

OBJECTIVE: To determine postural stability and proprioceptive postural control strategies of healthy subjects and subjects with recurrent low back pain (LBP) during acute inspiratory muscles fatigue (IMF).

SUMMARY OF BACKGROUND DATA: People with LBP use a more rigid proprioceptive postural control strategy than control subjects during postural perturbations. Recent evidence suggests that respiratory movements create postural instability in people with LBP. The role of the respiratory muscles in postural control strategies is unknown, but can be studied by inducing acute IMF.

METHODS: Postural control was evaluated in 16 people with LBP and 12 healthy controls, both before and after IMF. Center of pressure displacement was determined on a force plate to evaluate postural stability. Proprioceptive postural control strategies were examined during vibration of the triceps surae muscles or lumbar paraspinal muscles, while standing on both a stable and unstable support surface and without vision. Proprioceptive postural control strategies were determined by examining the ratio of mean center of pressure displacement measured during triceps surae muscles vibration to that measured during lumbar paraspinal muscles vibration. RESULTS.: After IMF, control subjects showed a significantly larger sway compared to the unfatigued condition while standing on an unstable support surface (P < 0.05). IMF induced an increased reliance on proprioceptive signals from the ankles, which resembled the postural control strategy used by people with LBP (P < 0.05). Subjects with LBP showed that same ankle steered postural control strategy in the unfatigued and IMF states (P > 0.05).

CONCLUSION: After IMF, control subjects use a rigid proprioceptive postural control strategy, rather than the normal "multisegmental" control, which is similar to people with LBP. This results in decreased postural stability. These results suggest that IMF might be a factor in the high recurrence rate of LBP.